feat: multi-account system

packages/app/src/ExternalStore.ts

@@ -0,0 +1,41 @@
+type HookFn = () => void;
+
+interface HookFilter {
+  fn: HookFn;
+}
+
+/**
+ * Simple React hookable store with manual change notifications
+ */
+export default abstract class ExternalStore<TSnapshot> {
+  #hooks: Array<HookFilter> = [];
+  #snapshot: Readonly<TSnapshot> = {} as Readonly<TSnapshot>;
+  #changed = true;
+
+  hook(fn: HookFn) {
+    this.#hooks.push({
+      fn,
+    });
+    return () => {
+      const idx = this.#hooks.findIndex(a => a.fn === fn);
+      if (idx >= 0) {
+        this.#hooks.splice(idx, 1);
+      }
+    };
+  }
+
+  snapshot() {
+    if (this.#changed) {
+      this.#snapshot = this.takeSnapshot();
+      this.#changed = false;
+    }
+    return this.#snapshot;
+  }
+
+  protected notifyChange() {
+    this.#changed = true;
+    this.#hooks.forEach(h => h.fn());
+  }
+
+  abstract takeSnapshot(): TSnapshot;
+}